In North Florida, it’s wise to select the more cold hardy citrus varieties. Kumquats and Satsuma mandarins are the most cold hardy of the edible citrus choices. In our area, it’s important to purchase citrus trees that are grafted onto trifoliate orange rootstock. Trifoliate orange produces inedible fruit but it’s the most cold hardy of all citrus. As a result, it is an excellent rootstock because it will tolerate colder temperatures and will convey its hardiness to the scion variety budded on it.
Because cold air drains downhill, avoid planting citrus trees in low areas. Higher elevations will be somewhat warmer. When it is an option, plant citrus trees on the south or southeast sides of a body of water where it will be warmer. Because most of our coldest weather comes from the north and northwest, citrus planted near the south side of the house will be better protected and the house may provide a microclimate, keeping citrus warmer.
During winter, it’s best to keep the soil under and around citrus trees bare of mulch and grass. And make sure to water early in the day before cold weather strikes. Bare, moist soil absorbs more heat during the day. This stored heat radiates upward during the night, keeping the citrus a little warmer. Mulch, traps this heat.
Banking (placing a mound of soil around the tree’s trunk to protect the graft union and lower trunk) is a cold protection practice for young citrus trees. Older trees can better withstand cold. To bank a tree, carefully mound soil free of weed seed and debris as high as reasonable, up into the scaffold limbs or higher whenever possible but at least cover the graft union. Build the bank before cold weather arrives and carefully remove it after danger of cold weather, which may be late February to mid-March. Completely remove all the added soil and be extremely careful to not damage the trunk with a shovel, hoe, etc. Materials, other than soil, used to wrap the trunk may kill the tree due to excessive trunk temperatures during warmer days.
Covering a plant without additional heat is a method to protect against frost rather than hard freezes. It may be difficult or impossible to cover large citrus trees but when covering young trees, drape the covering to the ground to trap heat under the covering. When covering plants, it’s best to use cloth rather than plastic. Remove the covering as soon as the cold has passed, preferably the next day. Leaving a plant covered day after day may cause the plant to break dormancy under the warm covering. This can result in increased cold injury the next time it freezes as compared to an uncovered plant.